WinForm Interview Questions

By | May 13, 2014

Windows Forms Interview Questions What base class do all Web Forms inherit from? System.Windows.Forms.Form W

hat is the difference between Debug.Write and Trace.Write? When should each be used? The Debug.Write call won’t be compiled when the DEBUGsymbol is not defined (when doing a release build). Trace.Write calls will be compiled. Debug.Write is for information you want only in debug builds, Trace.Write is for when you want it in release build as well.

Difference between Anchor and Dock Properties? Dock Property->Gets or sets which edge of the parent container a control is docked to. A control can be docked to one edge of its parent container or can be docked to all edges and fill the parent container. For example, if you set this property to DockStyle.Left, the left edge of the control will be docked to the left edge of its parent control. Additionally, the docked edge of  the control is resized to match that of its container control. Anchor Property->Gets or sets which edges of the control are anchored to the edges of its container.  A control can be anchored to one or more edges of its parent container. Anchoring a control to its parent ensures that the anchored edges remain in the same position relative to the edges of the parent container when the parent container is resized.

When would you use ErrorProvider control? ErrorProvider control is used in Windows Forms application. It is like Validation Control for ASP.NET pages. ErrorProvider control is used to provide validations in Windows forms and display user friendly messages to the user if the validation fails.  E.g  If we went to validate the textBox1 should be empty, then we can validate as below  1). You need to place the errorprovide control on the form  private void textBox1_Validating(object sender, System.ComponentModel.CancelEventArgs e) { ValidateName(); } private bool ValidateName() { bool bStatus = true; if (textBox1.Text == “”) { errorProvider1.SetError (textBox1,”Please enter your Name”); bStatus = false; } else errorProvider1.SetError (textBox1,””); return bStatus; }  it check the textBox1 is empty . If it is empty, then a message Please enter your name is displayed.

Can you write a class without specifying namespace? Which namespace does it belong to by default?? Yes, you can, then the class belongs to global namespace which has no name. For commercial products, naturally, you  wouldn’t want global namespace.

You are designing a GUI application with a windows and several widgets on it. The user then resizes the app window and sees a lot of grey space, while the widgets stay in place. What’s the problem?  One should use anchoring for correct resizing. Otherwise the default property of a widget on a form is top-left, so it stays at  the same location when resized.

How can you save the desired properties of Windows Forms application?  .config files in .NET are supported through the API to allow storing and retrieving information. They are nothing more than simple XML files, sort of like what .ini files were before for Win32 apps.

So how do you retrieve the customized properties of a .NET application from XML .config file?  Initialize an instance of AppSettingsReader class. Call the GetValue method of AppSettingsReader class, passing in the name of the property and the type expected. Assign the result to the appropriate variable.

Can you automate this process?  In Visual Studio yes, use Dynamic Properties for automatic .config creation, storage and retrieval.

My progress bar freezes up and dialog window shows blank, when an intensive background process takes over.  Yes, you should’ve multi-threaded your GUI, with taskbar and main form being one thread, and the background process being the other.

What’s the safest way to deploy a Windows Forms app? Web deployment: the user always downloads the latest version of the code, the program runs within security sandbox, properly written app will not require additional security privileges.

Why is it not a good idea to insert code into InitializeComponent method when working with Visual Studio?  The designer will likely through it away, most of the code inside InitializeComponent is auto-generated.

What’s the difference between WindowsDefaultLocation and WindowsDefaultBounds? WindowsDefaultLocation tells the form to start up at a location selected by OS, but with internally specified size. WindowsDefaultBounds delegates both size and starting position choices to the OS.

What’s the difference between Move and LocationChanged? Resize and SizeChanged?  Both methods do the same, Move and Resize are the names adopted from VB to ease migration to C#.

How would you create a non-rectangular window, let’s say an ellipse?  Create a rectangular form, set the TransparencyKey property to the same value as BackColor, which will effectively make the background of the form transparent. Then set the FormBorderStyle to FormBorderStyle.None, which will remove the contour and contents of the form.

How do you create a separator in the Menu Designer?  A hyphen ‘-‘ would do it. Also, an ampersand ‘&\’ would underline the next letter.

How’s anchoring different from docking?  Anchoring treats the component as having the absolute size and adjusts its location relative to the parent form. Docking  treats the component location as absolute and disregards the component size. So if a status bar must always be at the bottom no matter what, use docking. If a button should be on the top right, but change its position with the form being resized, use anchoring.

How do you trigger the Paint event in System.Drawing? Invalidate the current form, the OS will take care of repainting. The Update method forces the repaint.

With these events, why wouldn’t Microsoft combine Invalidate and Paint, so that you wouldn’t have to tell it to repaint, and then to force it to repaint? Painting is the slowest thing the OS does, so usually telling it to repaint, but not forcing it allows for the process to take place in the background.

How can you assign an RGB color to a System.Drawing.Color object? Call the static method FromArgb of this class and pass it the RGB values.

What class does Icon derive from?  Isn’t it just a Bitmap with a wrapper name around it? No, Icon lives in System.Drawing namespace. It’s not a Bitmap by default, and is treated separately by .NET. However, you can use ToBitmap method to get a valid Bitmap object from a valid Icon object.

Before in my VB app I would just load the icons from DLL. How can I load the icons provided by .NET dynamically?  By using System.Drawing.SystemIcons class, for example System.Drawing.SystemIcons.Warning produces an Icon with a  warning sign in it.

When displaying fonts, what’s the difference between pixels, points and ems?  A pixel is the lowest-resolution dot the computer monitor supports. Its size depends on user’s settings and monitor size. A point is always 1/72 of an inch. An em is the number of pixels that it takes to display the letter M

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